The present invention relates to a developing device for use in a printer, facsimile apparatus, copier or similar electrophotographic image forming apparatus and more particularly to an improved developing roller included in the developing device.
An electrophotographic image forming apparatus extensively used today includes a developing device for developing a latent image formed on an image carrier with toner. The developing device includes a developing roller for depositing the toner on the image carrier and a supply roller for supplying the developer from a hopper to the developing roller, as taught in, e.g., Japanese Patent Laid-Open Publication Nos. 63-189876 and 62-118372. The conventional developing roller includes a flexible member implemented by a single layer of urethane rubber or silicone rubber. Japanese Patent Laid-Open Publication No. 3-179369 discloses a developing roller including a porous flexible member whose hardness is less than 50.degree., as measured by an Ascar C hardness gauge.
However, the problem with the conventional developing devices is that the toner transfer from the supply roller to the developing roller differs from the opposite end portions to the intermediate portion. Such irregular toner transfer brings about various defective images including a black solid image with short density, a locally omitted image, and a mesh image with an irregular density distribution.
Technologies relating to the present invention are also disclosed in, e.g, Japanese Patent Laid-Open Publication Nos. 2-3078 and 4-75073.